The promoter(s) of the aromatase gene in male testicular cells.

ABSTRACT

Aromatase is the terminal enzyme responsible for estrogen biosynthesis in mammals; it is present in various testicular cells including germ cells. The aromatase gene (Cyp19) is unique in humans and its expression is regulated in a tissue and more precisely, in a cell-specific manner via the alternative use of various promoters located in the first exon. Nevertheless, there is little information concerning the regulation of the testicular aromatase especially in germ cells. This prompted us to study the control of Cyp19 gene expression and its role in the regulation of the testicular androgen/estrogen ratio. Gonadotrophins and cAMP modulate aromatase expression in somatic cells which confirms that promoter II is controlled via CRE. Moreover, we have demonstrated that in highly purified germ cells from adult rats (pachytene spermatocytes and round spermatids), transforming growth factor beta (TGFbeta) inhibited the expression of Cyp19 in both germ cell types. In contrast, tumor necrosis factor alpha (TNFalpha) stimulated Cyp19 expression in pachytene spermatocytes. The effect of TNFalpha is amplified in presence of dexamethasone. Therefore, we suggest that in germ cells, TNFalpha enhances expression of aromatase through promoter PI.4 in pachytene spermatocytes, possibly via an AP1 site upstream the GAS element, while in round spermatids TNF requires glucocorticoids as a co-stimulator to increase Cyp19 gene expression. In addition, we have shown that androgens and estrogens by themselves modulate Cyp19 gene expression in all testicular cell types studied suggesting the presence of ARE and ERE on the Cyp19 gene promoter(s). Finally, in presence of seminiferous tubules or Sertoli cell-conditioned media, aromatase transcripts are increased in both Leydig cells and germ cells suggesting that other locally produced modulators (e.g. LRH-1) are involved in the regulation of the aromatase gene expression especially in Leydig cells. Using RACE (Rapid Amplification of cDNA Ends)-PCR, we have confirmed that promoter II mainly directs expression of the aromatase gene in all testicular cell types studied in the rat. However, involvement of another promoter such as PI.4 is suggested as well.